That kind of reminds me of a Dave Allen joke I heard again the other day...
The Pope was arguing with an Atheist about the existence of God and failing to get his point across. They had been arguing for two hours and finally the Pope in frustration sat down.
"Listen," said the Pope, "You are like a man in a dark room, with no lights and windows, wearing a blindfold looking for a black cat that isn't there. What do you say to that?"
The Atheist thought for a moment.
"Yes your Holiness, you are probably right," he said, "but you are also like a man in a dark room, with no lights and windows, wearing a blindfold looking for a black cat that isn't there. The only difference is, you have found the cat."